Millikan Terminal Drop Charge Balance
An oil drop’s fall and rise speeds reveal its charge, while a holding field makes the force balance visible.
Free theory articleAn oil drop’s fall and rise speeds reveal its charge, while a holding field makes the force balance visible.
Concept & interpretation
The Millikan oil drop experiment involves observing tiny oil drops in a chamber where an electric field can be applied. By measuring the terminal speed of a drop falling under gravity and its terminal speed rising under an applied electric field, its charge can be inferred.
experiment
Explore the relationship between charge, drop radius, electric field, and terminal velocities in the interactive module:
https://riano.app/module/millikan-terminal-drop-charge-balance
- Set Drop radius to 0.5 and Charge units to 1.
- Set Selected field to 1 and Field mode to "Selected".
- Observe the calculated Terminal upward speed (approx 0.0505) and Inferred charge (1.0).
- Change the Field mode to "Hold if possible". Notice that the Terminal upward speed becomes exactly 0 as the field adjusts to exactly balance gravity.